Assets Acquired (Parenthetical) (Detail)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011
Significant Acquisitions and Disposals [Line Items]
Weighted average useful life of acquired intangible lease assets (in years)	14 years 1 month 6 days
Intangible lease assets-subject to amortization
Significant Acquisitions and Disposals [Line Items]
Weighted average useful life of acquired intangible lease assets (in years)	15 years	13 years 10 months 24 days

Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (a)(3)

-URI http://asc.fasb.org/extlink&oid=7658586&loc=d3e16265-109275

Name:	us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration